Alex's boyfriend, Karl, was punished by the Others in Room 23. It was a brainwashing room that flashed images to a prisoner in order to indoctrinate. I recall one of the parts proclaimed that:
GOD LOVES YOU AS HE LOVED JACOB ( superimposed on yellow carpeted stairs.)
With all the good and evil team concepts floating about cyberspace, Room 23 may be the best circumstantial evidence of who and what we can make of Jacob.
Room 23 was in the Hydra station. It was Dharma's room for psychological experiments. Apparently, it was taken over after the purge by the Others to indoctrinate new island arrivals. We think Walt was the only 815er to be held in that room. This could explain why the Others follow their leader without much discussion.
Now dissecting the reference to Jacob in the indoctrination tape:
God must represent the highest being in a pantheon.
Loves You: is directed toward the captive watching the video. It is used to comfort the person, to let their guard down, so as to reconfigure the person's core beliefs.
As He Loved: this is in the past tense, not the same present tense to the watcher. The screen could have said "as He loves Jacob" putting the person in the same category with God.
Jacob: Is a person/entity that has taken human form on the island and off the island. He has touched many people, and brought them to the island. One of the oldest touched people was Richard, who first thought the touch was a gift, but learned it was a curse.
Jacob could then represent the most famous person who lost God's favor: Satan.
Satan is an embodiment of antagonism that originates from the Abramhamic religions, being traditionally considered an angel in Judeo-Christian belief, and a Jinn in Islamic belief. Religions have used "Satan" as a name for the Devil. As the embodiment of evil, and plays a major role in Christian theology and literature, as well as in many other religions. He is the tempter and spiritual enemy of mankind. He is the adversary of God although subordinate to him and able to act only by his sufferance and is represented frequently as the leader or prince of all apostate angels and as ruler of Hell.
For most Christians, he is believed to be an angel who rebelled against God. Before his insurrection, Satan was among the highest of all angels. His pride is considered a reason why he would not bow to God as all other angels did, but sought to rule heaven himself. His ultimate goal is to lead people away from the love of God — to lead them to fallacies which God opposes. The Book of Revelation describes how Satan will be cast out of Heaven, down to the earth, having "great anger" and waging war against "those who obey God's commandments and hold to the testimony of Jesus." In mainstream Christianity he is called "the ruler of the demons," "the ruler of the world" and "the god of this world." Ultimately, Satan is thrown into the "lake of fire"not as ruler, but as one among many, being tormented day and night for all eternity.
Probably, the most effective way to convert followers of God is to subvert God's teachings. Hijack the belief system, so to speak, to become the spokesman of "good" while really using the power being gained by the followers acceptance of you for an "evil" uprising against God. If Jacob is Satan, he has used the mind games of good to con the Others and Candidates into believing he is good when in fact he is evil.
And what were the characteristics of the Devil in religious texts? Satan could shape shift into different forms on Earth. He was a serpent you tempted Eve to eat the forbidden fruit of knowledge, which led to the banishment of Adam and Eve from the Garden of Eden. That first sin against God's word evolved a world in which Satan could have influence - - - temptations, sins, crime, murder, pain, suffering . . . but maybe Satan's days of messing with humans has grown tired, and he wants his ultimate revenge: the war to retake heaven.
That last paragraph sounds more like the motivation of MIB. It could be. Satan had a band of rebellious angels who were cast out of heaven. His henchmen or minions could be his followers doing his dirty work (with lower beings like humans). Maybe MIB is tired of being a demonic gangster, and wants to return to heaven not to overthrow it, but to seek forgiveness.
This would put the story clearly in the lines of the Nexus Buffer Theory, where the island is a nexus point between heaven and hell, and the potential final battlefield between the forces of good and evil.